Seeding implements typically comprise a plurality of furrow openers mounted on an implement frame. The furrow openers are spaced laterally across the width of the implement in generally parallel opener rows extending perpendicular to the operating travel direction. The openers are typically mounted in opener rows on horizontal frame members that are oriented perpendicular to the operating travel direction. There are typically three or four opener rows spaced from the front of the implement to the rear thereof. When the implement is travelling in the operating travel direction the opener rows are perpendicular to the operating travel direction, and the furrows made by the openers are thus parallel to each other and equally spaced across the width of the implement at the designed furrow spacing.
Thus in order to maintain the correct furrow spacing, the implement must move in the operating travel direction in such a manner that the opener rows are perpendicular to the travel direction. Often however uneven forces acting on the implement cause the implement to skew, such that the opener rows are at an angle to the operating travel direction that is not perpendicular, but inclined in one direction or the other. These forces are caused by unequal soil conditions across the width of the implement, uneven ground penetration of ground engaging tools on the implement, uneven wear on ground engaging tools, by gravity when travelling on hill sides, and like conditions. While some of these forces are relatively constant, most are constantly changing. Such skewing has the undesirable effect of altering the furrow spacing.
The spacing of the furrow opener on each opener row of course stays the same, but as the opener rows incline with respect to the travel direction the lateral spacing of the furrows made by the openers on the same row will decrease somewhat. This is not usually significant however the lateral location of the furrow openers on the rear rows can change significantly with respect to the lateral location of the furrow openers on the front rows. The longer the distance between the front opener row and the rear opener row, the greater the change in the spacing of the furrows made by the furrow openers on the front opener row and those made by openers on the rear opener row. Spacing increases between some furrows and decreases between others.
Such skewing also causes the implement to travel offset from the centerline of the tractor, such that when making back and forth passes across a field, the implement is offset with respect to the tractor. Thus when using a Global Positioning System (GPS) guidance system, or automatic steering system that guides the tractor, such skewing will cause an overlap going one way and a miss going the other way. Between row seeding as described in the present inventor's U.S. Pat. No. 6,553,925 is also problematic when excessive skewing occurs.
While skewing is a particular concern with seeding implements, row crop cultivation requires accurate guiding of ground engaging tools such as cultivator shovels, blades, and discs, and similar problems arise when these implements travel in a skewed orientation.
The problem has been addressed in U.S. Pat. No. 7,147,241 to Beaujot et al. In the Beaujot system a sensor member is located in about the middle of the furrow openers on the implement. The sensor is shown as a wheel that rolls in the operating travel direction. The wheel is mounted on a trailing arm that pivots at a front end thereof about a vertical axis. Thus when the arm is positioned at a 90 degree angle relative to the horizontal bars of the implement frame to which the furrow openers are mounted, it is considered to be in the neutral position and the seeding implement is in alignment with no skew. If the implement skews, the horizontal bars incline from the perpendicular orientation and the sensor detects this skew and sends a steering signal to steerable rear wheels on the implement which steer the rear end of the implement to one side or the other to correct the skew. Such steering wheels add significantly to the cost and complexity of the implement.
Skew is also corrected using heavy coulter discs or coulter wheels which are oriented to roll in the operating travel direction and penetrate the soil such that the discs exert a force against the soil that resists lateral movement and thus reduces skewing. These coulters can also be oriented at an angle to the operating travel direction and moved up and down into the soil as needed to correct skew, in much the same manner as with the steering implement wheels of Beaujot. Such an angled vertically movable coulter on each side of the implement can move the implement laterally in either direction to correct skew. These coulters disturb the soil in a manner that is undesirable in minimum and no tillage farming operations.
It is also known to detect skew by using two GPS sensors one located forward and one rearward on the implement or tractor and implement. The sensors are aligned in the operating travel direction and when skew occurs this alignment changes and the sensors are no longer following the same path. This deviation is detected and a correction signal can be sent to correction mechanisms such as the steering wheels or coulters described above.
The known means for detecting and correcting implement skewing are relatively costly and complex, and have undesirable consequences for some farm operations.